Among the co-sponsors of the bill is Rep. Andy Harris, the lone Republican in Maryland's congressional delegation.

The bill, known as the Marriage Protection Amendment, asks for the words "marriage in the United States shall consist only of the union of a man and a woman" to be added to the Constitution and would prevent state constitutions to require marriage to be "conferred upon" same-sex couples.

Yet even though a majority of Maryland voters approved legalizing same-sex marriage in a 2012 ballot measure, Harris' district (which covers the entire Eastern Shore and portions of Baltimore, Harford and Carroll counties) actually voted against the ballot measure. It's those constituents who Harris represents in Congress, which puts his co-sponsorship of the Marriage Amendment in perspective.

For Harris' bill to become the 28th amendment, two-thirds of both the House and Senate would need to approve it -- and then all but 12 states would need to ratify it. Currently, 13 states have legalized same-sex marriage.